A level chemistry group 7

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  • Group 7
    • Halides
      • Reducing agent: reducing power increases due to e_ distance + shielding increasing so weaker attraction makes it easier to lose an e-
      • Sulfuric acid: all halides react with conc H2SO4 to give a HX to begin with. Some halides can reduce further
        • NaF/NaCl: Produces NaHSO4(s) + HCL/HF(g)   misty fumes
        • NaBr: first reaction is the same but the HBr reduces sulfuric acid:  2HBr(aq) + H2SO4(l) => Br2(g) + SO2(g) + 2H2O(l)        chocking fumes of SO2 and orange fumes of Br2
        • NaI: same 1st reaction, same 2nd reaction (produces grey I2(s)+purple gas
          • HI reduces the SO2 to H2S  (bad egg smell) 6HI(g) + SO2(g) => H2S(g) + 3I2(s) + 2H2O(l)
      • Testing for halides: add dilute nitric acid then silver nitrate solution to form a precipitate Ag+(aq) + X-(aq) => AgX(s) chloride: white bromide: cream  iodide: yellow
        • add ammonia solution(NH3,aq,)              Cl- dissolves in dilute NH3, Br- dissolves in conc NH3, I- insoluble in conc NH3
    • Halogens
      • Properties down the group: boiling point increases due to Van der Waals forces   electronegativity decreases.....shielding+e- distance      colour gets darker         less reactive
      • Displacement: halogens are oxidising agents, less oxidising down group    a halogen will displace a halide that's below it in the periodic table
        • chlorine will displace bromide (orange solution) and iodide (brown solution) bromine will displace iodide(brown solution)
      • chlorine
        • Disproportion when Cl2 reacts with H2O to produce 2H*+(aq), Cl*-(aq), 1/2O2(g)
          • Sunlight > decompose to form chloride ions and O2
        • Disproportion of Cl2 (reduced and oxidised) to produce bleach,NaCl22NaOH(aq) +Cl2(g) => NaClO(aq) + NaCl(aq) + H2O(l)
        • chlorate(I) ions kill bacteria ( in ClO), so can be added to water to make it safe in low concentration


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